If you do not limit the heating of water in the boiler and pipelines, then it boils and passes into the vapor phase, causing the pressure in the network to rise to a critical level. The result is a rupture of the line or casing of the heat generator and complete steam room. To prevent the described emergency situation, a safety valve is used to relieve pressure in the heating system in advance. So, special attention should be paid to the selection of this important element, in which this material will help you.
Most ordinary users who are faced with closed water heating systems are familiar with only one type of safety valve - a simple spring-loaded valve with a fixed setting, shown in the photo. The reason is clear - these products are installed everywhere on any boilers, since they are part of the safety group along with a pressure gauge and an air vent.
Note. Wall-mounted heat generators operating on electricity and natural gas are equipped with safety elements from the factory. They are placed inside the case and are not visible from the outside.
Let's understand how a conventional emergency valve, shown in the diagram above, works:
- Under normal conditions, the diaphragm, attached to the stem and supported by a spring, sits tightly in the saddle and hermetically closes the passage.
- If the coolant overheats, it expands and creates excess pressure in the closed system, partially compensated by the expansion tank.
- When the amount of water backwater reaches the threshold of the valve (usually - 3 Bar), the spring is compressed under its influence and the membrane opens the passage. The automatic discharge of the boiling coolant is carried out until the spring has enough force to close the flow area again.
- In the event of an emergency, the owner of the house can relieve excess pressure himself by turning the handle on the top of the product.
A few words about where the relief valve is placed along with the safety group in a closed heating system. Its place is on the section of the supply line in the immediate vicinity of the boiler (recommended no further than 0.5 m).
An important point. It is forbidden to install taps, valves and other blocking devices on the pipeline leading from the heat generator to the safety elements.
It is not worth it to tightly connect the pipe of the product to the sewer - wet spots or puddles will indicate valve operation and problems in the heating network. For example, the expansion tank failed or the circulation pump failed when working with a solid fuel boiler (perhaps the electricity was turned off). Often the device begins to leak due to debris getting between the seat and the plate. Learn more about his work in this video:
Clarifying information. Relief spring valves are called subversive by craftsmen and installers, because the pressure of the coolant compresses the spring and causes the membrane to undermine. Do not confuse them with explosive elements installed on the chimneys of industrial boilers burning natural gas.
Types of safety valves
The traditional demolition design described above is not perfect. The spring mechanism, driven by excessive pressure, is not accurate and may work late when the temperature in the boiler tank has reached 100 ° C and above, that is, boiling has begun. Of course, you can try to adjust the product with a screw or change the settings (there are versions with an adjusting cap), but this does not always give the desired effect.
Moment two: the safety valve for the boiler protects it from destruction, but not from overheating. After all, the discharge of the coolant does not allow to cool the heating unit if combustion in the furnace continues. And the last thing: in open-type heating systems, such devices are generally useless, since the water in them can boil without increasing pressure.
Leading manufacturers of heating fittings offer products of modern design, devoid of the listed disadvantages - thermal relief valves. These protective elements do not respond to an increase in water pressure in the system, but to an increase in its temperature to a critical level. There are 3 types of products:
- reset with a remote temperature sensor;
- combined device with a temperature sensor and a make-up circuit;
- the same with direct installation in the pipeline.
For reference. Here are the names of reliable brands, whose emergency fittings can be safely bought and used in private homes. These are the manufacturers ICMA and CALEFFI (Italy), Herz Armaturen (Austria) and the world famous European brand Danfoss.
The principle of operation for all varieties is the same: a spring mechanism with a membrane (or two) is driven by a bellows with a heat-sensitive liquid that expands significantly when heated. In this way, the thermal relief valves react quite accurately when the critical temperature is reached. We propose to consider each of them in more detail.
Element with remote sensor
The product is the same spring mechanism built into the body with two nozzles for connection to the supply line and discharge into the sewer. The rod that opens the plate and the way to the coolant is moved by bellows (2 groups - main and reserve). When the water overheats (from 95 to 100 °C), they are pressed by a thermosensitive liquid coming from the sensor flask through a capillary tube. The design of the safety element is shown in the figure:
The temperature valve is activated in three ways:
- with cooling through the water circuit of the heat generator;
- the same, through a special emergency heat exchanger;
- coolant discharge with automatic make-up.
The first scheme, shown below, is used for double-circuit heating installations that heat water for domestic hot water. When the sensor, mounted under the casing of the TT boiler, acts on the mechanism, the hot water from the circuit is drained into the sewer, and cold water from the water supply takes its place. Whatever the cause of the accident, such a flow system will quickly cool the boiler jacket and prevent the consequences.
Note. The publication uses schemes from the CALEFFI brand, taken from the official resource of the manufacturer.
The second scheme is intended for heat generators with built-in emergency heat exchanger for cooling in case of overheating. Such units are produced by European brands Atmos, Di Dietrich and others.
An example of connecting a waste element through a standard heat exchanger, see the video:
The latter scheme is implemented only together with an automatic make-up system, since here the valve discharges the coolant, and not the cooling water.
As you can see, the manufacturer allows the installation of two emergency means - for pressure (safety group) and for temperature (relief valve)
Warning. It is not recommended to use automatic make-up for wood-burning heaters with a cast iron firebox. The latter is afraid of temperature changes and can crack from supplying a large amount of cold water to the return line.
Combined products with make-up system
This bright representative of emergency valves is similar in principle to bypass valves and performs 3 functions at once:
- Discharge of superheated coolant from the boiler tank by a signal from a remote sensor.
- Efficient cooling of the heat generator.
- Automatic make-up of the heating system with cold water.
The picture above shows the design of the product, where it can be seen that 2 plates are installed on one rod, simultaneously opening 2 passages: the boiling coolant is discharged through the first, water flows through the second in the opposite direction and replenishes the losses. The connection diagram for a combined bypass valve with a solid fuel boiler looks like this:
Note. If it is necessary to use such a device for cooling a TT boiler with a cast-iron heat exchanger, then the flow must be organized through an open expansion tank or an indirect heating boiler.
A bypass valve with a triple outlet works according to the same combined principle, only it is built directly into the coolant supply pipeline near the heating unit. The bellows is located in the part of the body placed in the pipe. The discharge is made through the lower branch pipe, and the water supply and the make-up line are connected to the two upper ones. Such products are used when there is a lack of free space in the boiler room.
How to choose emergency fittings
Of course, at the price of purchase and installation, a traditional blast valve will cost less than temperature devices. It will easily protect a closed heating system tied to a gas, diesel or electric boiler, because in the event of an accident they stop heating almost instantly. Another thing is a wood-fired and coal-fired heat generator that cannot go out immediately.
To successfully select a thermal relief or overpressure valve, follow these guidelines:
- When using any energy source other than solid fuel, feel free to buy a conventional demolition device.
- Study the documentation of your heat source or boiler (depending on what needs to be protected) and select safety fittings according to the maximum allowable pressure indicated in it. Most of the heating equipment is designed for a limit of 3 Bar, although there are exceptions - Lithuanian Stropuva boilers can withstand only 2 Bar, and some Russian units (from inexpensive ones) - 1.5 Bar.
- For effective cooling of wood-fired heat generators in the event of an accident, it is better to install one of the heat relief valves. Their maximum working pressure is 10 bar.
- In open systems with a TT boiler, pressure relief is useless. Choose a safety product that operates at a coolant temperature of 95-100 ° C, suitable for your unit and make-up method.
Advice. Refrain from buying cheap safety fittings from China. Not only is it unreliable, it also leaks after the first explosion.
In addition to products with fixed settings, there are adjustable valves on the market. If you are not a professional in the field of heating, then you should not buy them, and there is no special need.
If you are keenly interested in the safety of the boiler room and the reliable operation of heating equipment, we recommend that you carefully study the range when buying fittings. The fact is that new useful products appear on the market that cannot be reviewed within the framework of this article, and they may come in handy for you.
operational moment. Monitor the condition of safety valves in order to detect the operation in time and understand the causes. Direct the heat release devices into the sewer funnel with a jet break - an unexpected splash of water in the boiler room and wet footprints will make it clear that an emergency has occurred.
